I am performing a science project, and this involves knowing the average operating altitude at which commercial passenger airplanes (jetliners) fly.
I am trying to find minimum operating altitudes and maximum operating altitudes of commercial airliners so that I can estimate an average operating altitude. Unfortunately, I can't find any documentation/papers/articles on the FAA website which give information on this. All I can find are blog articles and other informal articles, but I need something more concrete and formal to cite. Can anyone help?